1. Field
The present disclosure relates to a thermoelectric material, a thermoelectric element, a thermoelectric module including the thermoelectric material, and a method of preparing the thermoelectric material.
2. Description of the Related Art
The thermoelectric phenomenon is a reversible, direct energy conversion from heat to electricity and vice versa, which occurs due to movement of electrons and/or holes in a thermoelectric material.
Examples of the thermoelectric phenomenon include the Peltier effect, in which two dissimilar materials are connected and heat is released or absorbed due to a current applied from the outside, the Seebeck effect, in which an electromotive force is generated due to a temperature difference between the ends of the dissimilar materials that are connected, and the Thomson effect, in which heat is released or absorbed when a current is applied to a material having a temperature gradient.
By using the thermoelectric phenomenon, low-temperature waste heat may be directly converted to electricity, and the opposite is also possible. Thus, energy use efficiency may be increased. Also, the thermoelectric phenomenon may be applied in various fields, such as those related to a thermoelectric generator or a thermoelectric cooler.
Energy conversion efficiency of the thermoelectric materials is represented by a dimensionless figure of merit ZT defined by Equation 1:
                    ZT        =                                            S              2                        ⁢            σ            ⁢                                                  ⁢            T                    κ                                    Equation        ⁢                                  ⁢        1            
In Equation 1, ZT is a figure of merit, S is a Seebeck coefficient, σ is an electrical conductivity, T is an absolute temperature, and κ is a thermal conductivity.
To increase the energy conversion efficiency, a thermoelectric material having a high Seebeck coefficient, a high electrical conductivity, and a low thermal conductivity is desired, but generally, the Seebeck coefficient, the electrical conductivity, and the thermal conductivity have a trade-off relationship.
Because a nanostructure has a smaller particle size than a bulk material, an intergranular density of the nanostructure increases, which increases the scattering of phonons at an interface of the nanostructure. In this regard, thermal conductivity can be decreased, and the trade-off relationship between the Seebeck coefficient and the electrical conductivity may be destroyed due to the effects of quantum confinement, thereby improving the figure of merit.
Nanostructures are difficult to manufacture, and in bulk have a low figure of merit.
Therefore, there remains a need for a simple manufacturing process which provides a bulk quantity of a nanostructure having an improved figure of merit.